In a copending application by the inventor of the present invention, Ser. No. 813,442, a novel multi-element writing instrument is disclosed wherein successively selected writing elements are extended into writing position in response to the rotation of a selection unit to successive selection stations. Such an instrument finds its primary use in hand-held applications, wherein the user rotates the selection unit in accordance with the particular writing element desired. The separate writing elements may differ from each other in a number of ways, such as by color, by writing point, etc. For example, some may have ball point nibs while others have felt tip nibs, or the nibs may be of different width.
The writing instrument itself has a generally elongate body in which the individual writing elements are enclosed. In their non-selected positions, the elongate elements are uniformly spaced in a radial direction around the common axis of the instrument. Upon rotation of the selection unit, individual elements are displaced in a generally axial direction so that the writing nib of the selected element extends through the exit opening, preferably in alignment with the axis of the instrument.
In presently available computer-operated plotters or similar graphics systems such as, for example, flat bed systems, trend recorders etc., plotting may occur either by relative coordinate movement of the writing instrument and the paper, or by an arrangement whereby the paper remains stationary and the pen is capable of motion along coordinate axes. Additionally, the writing instrument is adapted to be selectively placed into contact with the paper, or withdrawn, by motion perpendicular to the plane of the paper.
The writing instrument may take different forms, e.g. pens with ball point or felt tip nibs, or capillary arms which feed ink from a reservoir to the writing point. Where multicolor writing is desired, the pens or capillary arms may be mounted in banks of relatively large size and the movement of the supporting arm on which the bank is mounted must take into account the spacing between respective pen nibs in order to bring the desired nib into writing position. Alternatively, the supporting arm may carry a turret at its end which turns selectively to bring different pens into writing position.
The physical size of a bank of pens may be considerable in relation to the space available within the physical dimensions of a plotter, so that the areas near the edge of the paper may not be accessible to all pens carried in the bank. While such a constraint may be avoided to some extent by the use of a turret, wherein the respective pens are held in a more compact manner, both the bank and the turret arrangement are cumbersome and mechanically complex. Further, due to the relatively large weight of these arrangements it becomes difficult to support the writing instrument at a distance and to control its position quickly and accurately. These arrangements are usually custom-fitted to a selected design configuration and they are not readily adaptable to other devices without major engineering changes.
As a general rule, plotters and similar graphics devices are expensive and require a relatively large capital investment. The cost of such equipment is increased still further where features are added which enable the equipment to plot in different colors. The implementation of these features is often cumbersome as already mentioned and is suitable primarily for use in large plotters. Thus, small plotters and other small graphics systems have heretofore been effectively limited to single color writing unless interruption by the operator was used. During the interval of operator intervention the equipment is idle. Further, such human intervention occasionally creats operational problems that bear on equipment reliability. Thus, with the advent of large multi-color plotters, smaller single-color plotters have been rendered obsolescent, notwithstanding the fact that many of these units remain in good operating condition.